Wellbores may be drilled into a surface location or seabed for a variety of exploratory or extraction purposes. For example, a wellbore may be drilled to access fluids, such as liquid and gaseous hydrocarbons, stored in subterranean formations and to extract the fluids from the formations. Wellbores used to produce or extract fluids may be lined with casing. A variety of drilling methods may be utilized depending partly on the characteristics of the formation through which the wellbore is drilled.
Some wellbores are reinforced with casing while drilling to stabilize the wellbore. Conventional casing is a steel or other metallic tubular that provides a durable surface for the interior of the wellbore. The casing allows downhole tools to be tripped into the wellbore with little or no damage to the integrity of the wellbore. The outer diameter of the casing is smaller than the drilled diameter of the initial wellbore, leaving an annular space around the casing and between the casing and wellbore. The annular space is filled with cement or other material that can harden and retain the casing in place relative to the wellbore. To cement the casing in place, the cement is pumped to the bottom of the casing and allowed to flow up the annular space.
To pump the cement to the bottom of the casing, a displacement fluid may be pumped behind the cement. A plug may be positioned between the displacement fluid and the cement to provide a barrier to pressure communication on either side of the plug. In drilling operations where full bore casing access is maintained during the operations, the casing may include an engagement feature, such as a plug landing nipple (PLN), on an inner surface of the casing. The plug can engage with the PLN by expandable dogs to limit prevent the longitudinal movement of the plug relative to the casing. The PLN and the plug may be positioned at or near the downhole end of the casing (or, in the case of horizontal drilling, the end of the casing farthest from the rig). After the cement cures, the plug may be milled away to allow further drilling or other operations through that portion of the wellbore.